Circuit interrupter with improved surge suppression

ABSTRACT

A circuit interrupter, such as a GFCI or AFCI product, is provided having a suppression and protection circuit and circuit interrupter circuitry. In one configuration, a semiconductor device and a voltage clamping device or surge protector, such as a metal oxide varistor (MOV), are utilized in the circuit interrupter for handling transient surges and overvoltage conditions. The semiconductor device, such as a SIDCA and a TVS diode, is connected to a solenoid or trip coil of the circuit interrupter circuitry to limit the amount of current through the semiconductor device. The MOV is placed between phase and neutral conductors of the circuit interrupter circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly owned application Ser. No.11/079,557, filed Mar. 14, 2005, now U.S. Pat. No. 7,082,021, entitledCircuit Interrupter with Improved Surge Suppression, which is acontinuation of application Ser. No. 09/829,339, filed Apr. 9, 2001, nowU.S. Pat. No. 6,900,972, both of which are incorporated herein in theirentirety by reference. This application is also related to the patentapplications which are related to U.S. Pat. No. 7,082,021 and identifiedtherein. These applications are the following:

This application is related to commonly owned application Ser. No.09/812,288, filed Mar. 20, 2001, now U.S. Pat. No. 7,049,910, entitledCircuit Interrupting Device with Reset Lockout and Reverse WiringProtection and Method of Manufacture, which is a continuation-in-part ofapplication Ser. No. 09/379,138 filed Aug. 20, 1999, now U.S. Pat. No.6,246,558, which is a continuation-in-part of application Ser. No.09/369,759 filed Aug. 6, 1999, now U.S. Pat. No. 6,282,070, which is acontinuation-in-part of application Ser. No. 09/138,955, filed Aug. 24,1998, now U.S. Pat. No. 6,040,967, all of which are incorporated hereinin their entirety by reference.

This application is related to commonly owned application Ser. No.09/812,875, filed Mar. 20, 2001, now U.S. Pat. No. 7,031,125, entitledReset Lockout for Sliding Latch GFCI, which is a continuation-in-part ofapplication Ser. No. 09/688,481 filed Oct. 16, 2000, now U.S. Pat. No.6,437,700, both of which are incorporated herein in their entirety byreference.

This application is related to commonly owned application Ser. No.09/813,683, filed Mar. 21, 2001, now U.S. Pat. No. 6,693,779, entitledIDCI With Reset Lockout and Independent Trip, herein incorporated in itsentirety by reference.

This application is related to commonly owned application Ser. No.09/812,601, filed Mar. 20, 2001, now abandoned, entitled Neutral SwitchTest Mechanism for a Circuit Interrupter, herein incorporated in itsentirety by reference.

FIELD OF THE INVENTION

The present invention relates to surge suppression, and in particular tocircuit interrupters, such as ground fault circuit interrupters (GFCI),arc fault circuit interrupters (AFCI) and related products with enhancedtransient suppression and protection characteristics.

BACKGROUND OF THE INVENTION

Circuit interrupters, such as GFCI and AFCI, are electronic devicesconnected to power lines. They require having protection against surgesknown to “travel” in power lines. UL 943 standard for GFCIs and UL 1699for AFCIs require these devices to pass unwanted tripping tests forcombination waveform and surge immunity tests at levels of 2 kV (1 kA),4 kV (2 kA) and 6kV (3 kA).

To protect circuit interrupting electronic devices against the powerline surge, it is commonly known to use MOV (metal oxide varistors)devices. MOV devices are capable of clamping voltage at a predeterminedlevel and dissipating surge energy up to another predetermined level.

Known circuit interrupting products typically include an MOV positionedacross the power lines of the circuit interrupting product, with the MOVproviding some surge protection to the circuit interrupting productcircuitry by clamping transient voltages to acceptable levels.

An MOV is typically a non-linear resistance that has a very highresistance below its threshold voltage and is typically modeled as anopen circuit. At voltages above the threshold voltage, the resistance isnearly zero and the voltage above the threshold is dissipated. Theamount of energy that an MOV dissipates is generally related to the sizeof the device, typically a disc or 9, 10, 14, 20, or 40 mm or the like.A larger MOV typically dissipates more energy, but takes up more space,may be more costly and may require more open space around the device.

The nature of the clamping and the amount of energy that may bedissipated is determined by the size of the disc and voltage ratingassociated with a disc type MOV. Heretofore, GFCl/AFCI and other circuitinterrupting products have typically been limited to handling transientvoltages of 6 kV at 3000 A.

When overvoltage conditions occur, protection components such as the MOVin the typical GFCI and AFCI may not survive, if they are selected toonly operate under 120V conditions. For example, a MOV in the typicalGFCI operating beyond its rating at overvoltage may disintegrate, andthus such conditions may also destroy the rest of the electronics in theGFCI product and possibly cause a fire. Furthermore, an MOV may fail byrupturing, exploding or igniting. Such failure conditions arepotentially dangerous.

Due to the requirements of circuit protection products withstandingabnormal overvoltage conditions, 120V devices cannot use MOV rated below230V-240V. In the event of surge pulses, such devices cannot clampvoltage fast enough so the peak voltage during surge can reach 600V-800Vwhich may cause electronic components of the devices to malfunction orthe device may trip which is undesired. For this reason, additionalprotection is needed to better protect GFCl/AFCI and other circuitinterrupting devices and satisfy UL standard requirements.

SUMMARY OF THE INVENTION

Accordingly, in view of the discussion above, there exists a need for asurge protection circuit which allows components such as a surgeprotector or voltage clamping device to survive power conditionsexceeding voltage and current ratings, and thus enabling a circuitinterrupting product, such as a ground fault circuit interrupter (GFCI)or arc fault circuit interrupter (AFCI) product to survive overvoltageconditions.

A suppression and protection circuit is used in conjunction with circuitinterrupter circuitry, such as circuitry in a GFCI or AFCI product. Inembodiments described herein, a surge protector or voltage clampingdevice, such as a metal oxide varistor (MOV), is utilized in the circuitinterrupting product for handling transient surges and overvoltageconditions. In embodiments described herein, the circuit interruptingproduct further includes the use of a semiconductor protection device inaddition to MOV.

In embodiments described herein, the semiconductor device is preferablyeither a TVS diode or a SIDAC (Silicon Diode for Alternating Current)marketed, for example, under the names SIDACtor, Transil or TSPD. Towork properly these semiconductor devices (in difference to MOV) requireto be in series with a current limiting component to limit possiblecurrent through them. The present disclosure provides embodiments wherea TVS or SIDAC is used with the solenoid or trip coil of the GFCI as thecurrent limiting component.

Nominal voltage for both TVS and SIDACs has to be selected to be above(or close to maximum) peak voltage applied to the circuit interrupterduring abnormal overvoltage. Therefore, TVS or SIDAC devices withnominal voltage of 350V/400V are preferable. Additionally, because ofthe nature of TVS and SIDAC devices of clamping voltage faster than MOVand because current through these devices is limited by the trip coil ofthe GFCI, the maximum voltage applied to the device electronics islimited to 400V-500V (depending on the semiconductor device used).

A preferred TVS diode for protection of a circuit interrupter, such as aGFCI product, is the SMBJ350CA manufactured by Littelfuse, Inc.,Chicago, Ill. A preferred SIDAC for protection of a circuit interrupteris the SIDACtor P350SCMCLRP also manufactured by Littelfuse, Inc.

In particular, in one embodiment according to the present disclosure,there is provided a circuit interrupter having a housing; at least oneinput conductor disposed at least partially within the housing andcapable of being electrically connected to a source of electricity; atleast one output conductor disposed within the housing and capable ofconducting electrical current to a load when electrically connected tosaid at least one input conductor; and circuit interrupter circuitrydisposed within the housing and configured to break the electricalconnection between the input and output conductors in response to theoccurrence of a ground fault or test cycle. The circuit interruptercircuitry includes a solenoid coil. The circuit interrupter further hasa surge protection circuit having a semiconductor device for reducingsurge voltage applied to the circuit interrupter circuitry. The solenoidcoil limits the current through the semiconductor device.

In an alternate embodiment, the circuit interrupter includes a resetmechanism is provided and is configured to reset the electricalconnection between the input and output conductors when the resetmechanism is activated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of a GFCI circuit having asuppression and protection circuit and a TVS diode according to a firstembodiment of the present disclosure;

FIG. 2 illustrates a schematic diagram of a GFCI circuit having asuppression and protection circuit and a SIDAC according to a secondembodiment of the present disclosure;

FIG. 3 illustrates a schematic diagram of a GFCI circuit having asuppression and protection circuit and a TVS diode according to a thirdembodiment of the present disclosure; and

FIG. 4 illustrates a schematic diagram of a GFCI circuit having asuppression and protection circuit and a SIDAC according to a fourthembodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A circuit interrupter having improved transient and overvoltagesuppression is described. The commonly owned U.S. patents referred toabove describe circuit interrupting devices and are incorporated hereinin their entirety by reference. For example, U.S. Pat. No. 7,049,910describes a circuit interrupting device having a reset mechanism with areset lockout portion. The reset lockout portion prevents thereestablishing of electrical continuity in open conductive paths if thecircuit interrupting portion is non-operational, if an open neutralcondition exists or if the device is reverse wired. The circuitinterrupter can be a GFCI and/or other related product having a circuitinterrupter, such as an AFCI and a fuse, event though the presentdisclosure refers mainly to a GFCI product.

The GFCI and/or related products, such as an AFCI, in accordance withthe present disclosure include a suppression and protection circuitwhich interfaces between power inputs and a ground fault circuitinterrupter (GFCI) circuit connected to a load. The GFCI and/or relatedproducts can also include a reset mechanism with a reset lockoutportion. The suppression and protection circuit providing enhancedsuppression of transient surges for the circuit interrupter as well asprotection from overvoltage conditions, while the circuit interrupter isoperational. The suppression and protection circuit 10 includes anovervoltage prevention circuit having a surge protector or voltageclamping device, such as a metal oxide varistor (MOV), and asemiconductor protection device, such as, for example, a TVS diode or aSIDAC (Silicon Diode for Alternating Current) marketed, for example,under the names SIDACtor, Transit or TSPD. The suppression andprotection circuit is described in greater detail with reference toembodiments shown by FIGS. 1-4.

FIG. 1 illustrates one example embodiment of the suppression andprotection circuit 10 and an interrupter or GFCI circuit 14 forming aGFCI product 100. The circuit 10 includes an MOV 22 positioned betweeninput power lines as the power inputs 12, for example, an alternatingcurrent (AC) line connection having a phase line 24 and a neutral line26. The lines 24, 26 are connected to phase line and neutral lineconductors 21, 23 of the GFCI 100.

The lines 24, 26 are also connected through the MOV 22 and through aground neutral transformer 28 and a differential or sensing transformer30 to the load 16, which may include two phase load connections 32′ and32″ and two neutral load connections 34′ and 34″. A test line 36 mayalso be provided in a manner known in the art including, for example, atest switch 38 and a resistor R4 having a 15 KOhms resistance.Optionally, a relay 40 and/or circuit breaker known in the art may beprovided, as further described herein, connecting the differentialtransformer 30 to the load lines 32′, 32″, 34′ and 34″.

A processor U1 of the GFCI circuit 14 is connected via a plurality ofpins or connectors to the transformers 28, 30 in a manner known in theart, for example, using capacitors C3 and C6-C9, resistor R4, and diodesZ1, Z2. In the example embodiment shown in FIG. 1, the resistor R3 has a100 ohm resistance, and the capacitors C3 and C6-C9 have capacitances of0.01 μF, 100 pF, 0.0033 μF, 10 μF, and 100 pF, respectively, each havinga voltage rating of 50 V, except for the capacitor C8 having a voltagerating of 6.3 V.

The processor U1 may be, for example, a model LM1851 ground faultinterrupter controller commercially available from “NATIONALSEMICONDUCTOR”, capable of providing ground fault protection for ACpower outlets in consumer and industrial environments. The processor U1is also connected via its pins/connectors to the MOV 22 in a mannerknown in the art, for example, using capacitors C10, C4 and C5 havingcapacitances of 0.01 μF, 1 μF, and 0.018 μF, respectively, at 50 V; acapacitor C2 having a 680 pF capacitance at 500 V; resistors R1 and R2having 15 kohms and 2 Mohms resistances, respectively; a diode D1; arectifier SC1 such as a silicon controlled rectifier (SCR); and a set ofdiodes D2-D5 forming a bridge diode circuit or configuration 42, asshown in FIG. 1.

The circuit 10 further includes a semiconductor protection device 50,such as a SIDAC D7 shown in FIG. 1 connected to the bridge diode circuit42 and to the neutral line 26. An optional snubber circuit (C1, R10) 52may be connected in parallel to the semiconductor protection device 50.The snubber circuit 52 can be used in addition to the describedprotection device 50 to improve the noise immunity by eliminating noise.

In the example embodiment shown by FIG. 1, the MOV 22 and thesemiconductor protection device 50 are connected to an inductor 44. Theinductor 44 may be a solenoid coil or bobbin acting as a trip coil, suchthat the inductor 44 also functions as an actuator to disengage therelay mechanism 40 on the load side. More specifically, the MOV 22provides primary protection against overvoltage conditions on the powerline and the semiconductor protection device 50 provides secondary andfaster protection. The inductor 44 or trip coil is used as a voltagedropping component or resistive component which is necessary foroperation of the semiconductor protection device 50.

In the embodiment shown in FIG. 1, the MOV 22 clamps the voltage exposedto the capacitor C1 to be within the voltage rating of the capacitor C1,for example, 400 V. As in the prior art, the MOV 22 itself in a GFCIproduct is capable of handling transient surges and overvoltageconditions of, for example, less than 2-6 kV at 3 kA surge. Using thesemiconductor protection device 50 in the disclosed suppression andprotection circuit 10, transient voltages exceeding, for example, 2 kVat 3 kA and even 6 kV at 3 kA, are suppressed. Accordingly, the MOV 22in the GFCI product is capable of handling voltages exceeding aroot-mean-square (RMS) voltage rating of the MOV 22, permitting the MOV22 to survive and provide primary protection from other transient,surge, and overvoltage conditions, as described herein.

During operation, the MOV 22 performs the functions of clamping andpassing surge current through its terminals, thereby protecting the restof the circuit interrupter circuitry. However, the MOV 22 reacts tooslowly to the overvoltage condition compared to the semiconductorprotection device 50. Therefore, at the beginning of the surge pulse,the voltage applied to the circuit interrupter circuitry may reach 800Vor more causing the destruction of the GFCI product without the use ofthe device 50. The semiconductor protection device 50 provides secondaryprotection to prevent the destruction of the GFCI product. The device 50performs the function of clamping the excess voltage much fastercompared with the MOV 22, such that the GFCI product gets exposedvoltage drops below 400-500V. The inductor 44 or trip coil is used as aresistive component to perform the functions of dropping the excessvoltage and limiting current through the semiconductor protection device50. In this manner, the surge suppression and overvoltage protection ofa GFCI product which includes the circuit 10 and the GFCI circuit 14 issignificantly improved.

Referring to FIGS. 2-4, other sample embodiments of other GFCI productsin accordance with the present disclosure are described. The operationand functions of the MOVs 22′, 22″ and 22′″ and the operation andfunctions of the semiconductor protection devices 50′, 50″ and 50′″ aresimilar, if not identical, to the operation and functions of the MOV 22and semiconductor protection device 50, respectively. In FIG. 2, theGFCI product 100′ is similar to the GFCI product 100 except forincluding a TVS D7′ as the semiconductor protection device 50′. The MOV22′ is a variable resistance that may have an effect as voltage changes.

In FIG. 3, as in the first embodiment shown by FIG. 1, the GFCI product100″ includes a semiconductor protection device 50″ which is a SIDACD7″. The device 50″ is connected to the bridge diode circuit 42 and toground. The MOV 22″ is a variable resistance that may have an effect asvoltage changes.

In FIG. 4, as in the second embodiment shown by FIG. 2, thesemiconductor protection device 50′″ is a TVS D7′″. The device 50′″ isconnected to the bridge diode circuit 42 and to ground. The MOV 22″ is avariable resistance that may have an effect as voltage changes.

TVS diodes and SIDAC are manufactured in small SMT packages (SMA (400 W)and SMB (600 W)). This allows MOV miniaturization to createsemiconductor protection devices in small housings capable of fittinginto a standard wall box.

Voltage clamping devices include without limitation selenium cells,Zener diodes, silicon carbide varistors and metal oxide varistors(MOVs).

Additionally, it is known in the art to provide a visual indication thata device equipped with surge suppression is still operating with surgesuppression capability. In an embodiment of the present invention, avisual indicator is provided to indicate that the device is operatingwith adequate surge suppression capability. Similarly, an alarm such asan audio indicator may be provided to indicate that the device is nolonger operating with adequate surge suppression capabilities.

While there have been shown and described and pointed out thefundamental features of the invention, it will be understood thatvarious omissions and substitutions and changes of the form and detailsof the device described and illustrated and in its operation may be madeby those skilled in the art, without departing from the spirit of theinvention.

1. (canceled) 2-25. (canceled)
 26. A circuit interrupter, comprising:circuit interrupter circuitry for breaking an electrical connectionbetween input and output conductors in response to the occurrence of afault; and a surge protection circuit electrically coupled to thecircuit interrupter circuitry, the surge protection circuit including atransient voltage suppression (TVS) diode arranged to reduce surgevoltage applied to the circuit interrupter circuitry, wherein saidcircuit interrupter circuitry further comprises a solenoid coil arrangedto limit current through the TVS diode.
 27. The circuit interrupter ofclaim 26, wherein the fault includes one of an actual fault and asimulated fault.
 28. The circuit interrupter of claim 26, furthercomprising a metal oxide varistor (MOV) electrically disposed to provideprimary protection against an over-voltage condition.
 29. The circuitinterrupter of claim 26, wherein the TVS diode is arranged to providesecondary protection against an over-voltage condition.
 30. The circuitinterrupter of claim 26, further comprising a bridge diode circuitelectrically coupled between the TVS diode and the solenoid coil. 31.The circuit interrupter of claim 30, wherein the solenoid coil isarranged and configured to impose a voltage drop.
 32. The circuitinterrupter of claim 26, further comprising an RC circuit, wherein theTVS diode is electrically coupled in parallel to the RC circuit.
 33. Thecircuit interrupter of claim 26, wherein the circuit interrupter is linepowered.
 34. The circuit interrupter of claim 26, wherein the TVS diodehas a clamping voltage of 400 Volts or less.
 35. A circuit interrupter,comprising: circuit interrupter circuitry for breaking an electricalconnection between input and output conductors in response to theoccurrence of a fault; and a surge protection circuit electricallycoupled to the circuit interrupter circuitry, the surge protectioncircuit including a silicon diode for alternating current (SIDAC) forreducing surge voltage applied to the circuit interrupter circuitry,where a SIDAC voltage exceeds a normal power line voltage, wherein thecircuit interrupter circuitry further comprises a solenoid coil arrangedto limit current through the SIDAC.
 36. The circuit interrupter of claim35, wherein the fault includes one of an actual fault and a simulatedfault.
 37. The circuit interrupter of claim 35, further comprising ametal oxide varistor (MOV) electrically disposed to provide primaryprotection against an over-voltage condition.
 38. The circuitinterrupter of claim 35, wherein the SIDAC is arranged to providesecondary protection against an over-voltage condition.
 39. The circuitinterrupter of claim 35, further comprising a bridge diode circuitelectrically coupled between the SIDAC and the solenoid coil.
 40. Thecircuit interrupter of claim 39, wherein the solenoid coil is arrangedand configured to impose a voltage dropping component.
 41. The circuitinterrupter of claim 35, further comprising an RC circuit, wherein theSIDAC is electrically coupled in parallel to the RC circuit.
 42. Thecircuit interrupter of claim 35, wherein the circuit interrupter is linepowered.
 43. The circuit interrupter of claim 35, wherein the SIDACdiode has a clamping voltage of 400 Volts or less.
 44. A circuitinterrupter having input and output conductors, the circuit interruptercomprising: interrupter circuitry for breaking an electrical connectionbetween the input and output conductors in response to the occurrence ofa fault; a surge protection circuit electrically coupled to theinterrupter circuitry and configured to reduce surge voltage applied tothe interrupter circuitry, the surge protection circuit including asemiconductor device and an inductor, wherein the inductor limitscurrent through the semiconductor device; and wherein the semiconductordevice is one selected from the group consisting of a silicon diode foralternating current (SIDAC) and a transient voltage suppression (TVS)diode, where a SIDAC voltage exceeds a normal power line voltage. 45.The circuit interrupter of claim 44, wherein the TVS diode or the SIDACis arranged to provide secondary protection against an over-voltagecondition.
 46. The circuit interrupter of claim 44, further comprising abridge diode circuit electrically coupled between the TVS diode and theinductor or between the SIDAC and the inductor.
 47. The circuitinterrupter of claim 44, wherein the circuit interrupter is linepowered.
 48. The circuit interrupter of claim 44, wherein the TVS diodeor the SIDAC has a clamping voltage of 400 Volts or less.